It is much more involved than I expected. I find this impressive.
Why did you choose that approach rather than compiling a modified kernel that would do what you want? The latter seems easier to me and also safe because you can always write back the original kernel on the SD card (assuming it is a SD card and not eMMC).
The newer kobos don't have the /dev/kmem device.
Code:
[root@kobo ~]# gunzip -c /proc/config.gz | grep CONFIG_DEVKMEM
# CONFIG_DEVKMEM is not set